About the Author:Aleksandar Jurisic received his Ph.D. from the University of Waterloo in 1995. He held a two year industrial post doctoral position at Certicom Corp., Canada and the department of Combinatorics and Optimization at the University of Waterloo, Canada, working in cryptography and algorithmic number theory and a one-year research position at Institute of Mathematics, Physics and Mechanics (IMFM), at the University of Ljubljana, Ljubljana, Slovenia. After that he became an occasional teacher of cryptography and computer security, and a researcher at the IMFM, Ljubljana. His main research interests are discrete mathematics and geometry. He loves problem solving and trying to make difficult things look easy. In his free time he enjoys biking (mostly mountain Krim), playing basketball and teaching recreational mathematics. He wrote a problems book for mathematics competitions in '89. In 2005 he co-founded the Slovenian Society of Cryptology.